In general, the conventional method of sterilizing the canned food involves the use of steam to expel the air in a sterilizing kettle until such time when the content of air in the sterilizing kettle drops to a certain level and when the temperature in the sterilizing kettle conforms to a given standard. Thereafter, the steam is introduced continuously into the sterilizing kettle so that the temperature in the sterilizing kettle is increased to reach a given level at which the living microorganisms in the canned food are killed. Upon the completion of such a sterilizing process as described above, the canned food so sterilized is finally subjected to a pressurized cooling or water cooling as required.
The conventional steam method of sterilizing the canned food is not cost-effective, in view of the fact that the steam used to expel the air in the sterilizing kettle amounts to almost one third of the total of the steam which is used in the entire process of sterilizing the canned food, and that the steam left in the sterilizing kettle is finally released into the atmosphere at the conclusion of the sterilizing process. It is readily apparent that the used steam is not recycled at any given stage of the conventional sterilizing process of the canned food. In other words, the energy efficiency of the above-mentioned conventional method of sterilizing the canned food remains to be improved.